Solar wind as the origin of rapid reddening of asteroid surfaces.

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Bibliographic Details
Title:	Solar wind as the origin of rapid reddening of asteroid surfaces.
Authors:	Vernazza, P., Binzel, R. P., Rossi, A., Fulchignoni, M., Birlan, M.
Source:	Nature. 4/23/2009, Vol. 458 Issue 7241, p993-995. 3p. 3 Graphs.
Subjects:	Astronomy, Asteroids, Spectral reflectance, Optical reflection, Solar wind, Weathering, Silicates spectra, Particle size distribution
Abstract:	A comparison of the laboratory reflectance spectra of meteorites with observations of asteroids revealed that the latter are much ‘redder’, with the spectral difference explained by ‘space weathering’, though the actual processes and timescales involved have remained controversial. A recent study of young asteroid families concluded that they suffered only minimal space weathering. Here we report additional observations of those families, revealing that space weathering must be a very rapid process—the final colour of a silicate-rich asteroid is acquired shortly after its ‘birth’ (within 106 years of undergoing a catastrophic collision). This rapid timescale favours solar wind implantation as the main mechanism of space weathering, as laboratory experiments have shown that it is the most rapid of several competing processes. We further demonstrate the necessity to take account of composition when evaluating weathering effectiveness, as both laboratory and asteroid data show an apparent dependence of weathering on olivine abundance. The rapid colour change that we find implies that colour trends seen among asteroids are most probably due to compositional or surface-particle-size properties, rather than to different relative ages. Apparently fresh surfaces most frequently seen among small near-Earth asteroids may be the result of tidal shaking that rejuvenates their surfaces during planetary encounters. [ABSTRACT FROM AUTHOR]
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Database:	Psychology and Behavioral Sciences Collection

Description
Abstract:	A comparison of the laboratory reflectance spectra of meteorites with observations of asteroids revealed that the latter are much ‘redder’, with the spectral difference explained by ‘space weathering’, though the actual processes and timescales involved have remained controversial. A recent study of young asteroid families concluded that they suffered only minimal space weathering. Here we report additional observations of those families, revealing that space weathering must be a very rapid process—the final colour of a silicate-rich asteroid is acquired shortly after its ‘birth’ (within 106 years of undergoing a catastrophic collision). This rapid timescale favours solar wind implantation as the main mechanism of space weathering, as laboratory experiments have shown that it is the most rapid of several competing processes. We further demonstrate the necessity to take account of composition when evaluating weathering effectiveness, as both laboratory and asteroid data show an apparent dependence of weathering on olivine abundance. The rapid colour change that we find implies that colour trends seen among asteroids are most probably due to compositional or surface-particle-size properties, rather than to different relative ages. Apparently fresh surfaces most frequently seen among small near-Earth asteroids may be the result of tidal shaking that rejuvenates their surfaces during planetary encounters. [ABSTRACT FROM AUTHOR]
ISSN:	00280836
DOI:	10.1038/nature07956